Steam turbine cycle

ABSTRACT

A steam turbine cycle of the present invention comprises a high pressure turbine  1 , a reheating turbine  24 , a boiler  4 , feed heaters  6  for heating a feed water to the boiler  4  by a bleed steam from the turbines  1  and  24 , a feed pump  12 , and a condenser  10 , the steam turbine cycle being a single-stage reheating cycle where a working fluid is water and using a Rankine cycle which is a regenerative cycle. A steam temperature at an outlet of the boiler is 590° C. or more. A temperature increase ratio between: a feed-water temperature increase in a first feed heater  7  corresponding to a bleed steam (high-pressure turbine exhaust bleed steam)  22  from an exhaust steam of the high pressure turbine  1 ; and an average of feed-water temperature increases in second feed heaters  8  where a pressure of the feed water is lower than that of the first feed heater  7 ; falls within 1.9-3.5.

FIELD OF THE INVENTION

The present invention relates to a steam turbine cycle having animproved cycle thermal efficiency.

BACKGROUND ART

An example of a steam turbine cycle used in a heat power plant or thelike is described as a conventional art with reference to FIG. 1.

A boiler feed water 14 heated by a boiler 4 with the use of fuelcombustion heat so as to generate a superheated steam (hereinafterreferred to as “main steam 16”) of a sufficiently high temperature. Thesuperheated steam may be an ultra supercritical pressure fluid.

The main steam 16, which has flown into a high pressure turbine 1,expands and flows therethrough, while a pressure and a temperaturethereof are lowered.

Most part of a high-pressure turbine exhaust steam 21, which has flownout from the high pressure turbine 1, flows into a reheater 5, andbecomes there a reheated steam 17 of a higher temperature. The reheatedsteam 17 flows into an intermediate pressure turbine 2.

The steam expands and flows through the intermediate pressure turbine 2,while a pressure and a temperature thereof are lowered. Then, the steamflows into a low pressure turbine 3.

The steam expands and flows through the low pressure turbine 3, while apressure and a temperature thereof are lowered. A part of the steamoften becomes a saturated steam as a liquid water. The saturated steamis cooled by a condenser 10 by using sea water or atmospheric air 23, sothat the saturated steam becomes a condensed water 25. The condensedwater 25 is sent to a feed heater 6 by a condensing pump 11 to become aboiler feed water 14. The intermediate pressure turbine 2 and the lowpressure turbine 3 constitute a reheating turbine 24.

In FIG. 1, eight feed heaters 6 are illustrated. The boiler feed water14 is heated by a bleed steam 20 bled from bleeding positions 31 inchannels of the intermediate pressure turbine 2 and the low pressureturbine 3. A bleed steam of a higher pressure is flown into the feedheater 6 of a higher pressure.

In FIG. 1, the low pressure turbine 3 is illustrated as a double flowpressure turbine, and a steam is bled from only one of the low pressureturbine 3. However, a steam is actually bled from both the low pressureturbines 3 and merged. The merged steam flows into the feed heater 6. Itis possible to bleed a steam from one of the low pressure turbines 3,depending on the feed heater 6.

The feed heater 6 is classified into a feed heater of a surface type anda feed heater of a mixing type. In a feed heater of a surface type, thebleed steam 20 is condensed by exchanging heats with a feed water via aheat transmission surface to become a drain water 15. In principle, thedrain water 15 sequentially flows from the feed heater 6 of a higherpressure to the feed heater 6 of a lower pressure. The drain water 15 inthe feed heater 6 of the lowest pressure flows into the condenser 10.The drain water 15 may be merged into a feed water by a drain water pump13.

In the feed heater of a mixing type, a bleed steam is directly mixedwith a feed water to heat the same. A deaerator 9 for deaerating oxygenor the like which is dissolved in a feed water is included in the feedheater of a mixing type.

In order to send a feed water to a feed heater 6 of a higher pressure, afeed pump 12 is disposed directly downstream of the feed heater of amixing type. In FIG. 1, although a bleed steam to the feed heater of amixed type is an intermediate-pressure turbine exhaust bleed steam 32,another steam is possible. The deaerator 9 may be omitted. Even when thedeaerator 9 is omitted, the feed pump 12 is disposed on a suitableposition between the plurality of feed heaters 6. A feed watersequentially heated in all of the feed heaters 6 flows into the boiler4.

In FIG. 1, the high pressure turbine 1, the intermediate pressureturbine 2, and the low pressure turbine 3 are connected to each other bya single rotation shaft 19, and are connected to a generator 18. A steamexpands in the high pressure turbine 1, the intermediate pressureturbine 2, and the high pressure turbine 3, so that enthalpy of thesteam is converted into a shaft power, whereby electric power isgenerated by the generator 18. It is possible not to connect therespective turbines to the single generator 18 by connecting theturbines by the single rotation shaft 19.

FIG. 1 illustrates the low pressure turbine 3 as a double flow pressureturbine in which a flow-in steam is divided into two and the dividedsteams flow into the two low pressure turbines 3. The flow-in steam maybe divided into four, or may not be divided. In FIG. 1, although theintermediate pressure turbine 2 is illustrated as a single flow pressureturbine, the intermediate pressure turbine 2 may be a double flowpressure turbine. In addition, although FIG. 1 shows that theintermediate pressure turbine 2 and the low pressure turbine 3 areseparated turbines, a single reheating turbine 24 is possible.

Both of a regenerative cycle using the bleed steam 20, and a reheatingcycle in which the high-pressure exhaust steam 21 heated by the reheater5 flows into the reheating turbine 24, are modified Rankine cycles, andimprove a thermal efficiency from a simple Rankine cycle. In a powergeneration plant, a thermal efficiency is substantially equal to a valueobtained by dividing an amount of generated power by an amount of boilerheat input.

In addition to a cycle structure, a cycle thermal efficiency variesdepending on a temperature and a flowrate of each bleed steam 20. Inparticular, in accordance with advancement of a material against a hightemperature, a temperature of steam has been recently more and moreincreased, whereby a cycle thermal efficiency has been improved.However, there still is a room for approving a cycle structure underhigh temperature conditions of steam.

The below non-patent document describes that “an optimum performance isobtained when an increase in enthalpy of a certain heater caused by ableed steam from a reheating point is 1.8 times an average increase inenthalpy in heaters of a pressure lower than that of the certainheater”.

Non-Patent Document: “Steam Turbine Performance and Economics” writtenby Bartlett

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The object of the present invention is to provide a steam turbine cycleof an improved cycle thermal efficiency.

Means for Solving the Problem

The invention according to claim 1 is a steam turbine cycle comprising ahigh pressure turbine, a reheating turbine, a boiler, feed heaters forheating a feed water to the boiler by a bleed steam from the highpressure turbine and the reheating turbine, a feed pump, and acondenser, the steam turbine cycle being a single-stage reheating cyclewhere a working fluid is water and using a Rankine cycle which is aregenerative cycle, wherein a steam temperature at an outlet of theboiler is 590° C. or more, and a temperature increase ratio between: afeed-water temperature increase in a first feed heater corresponding toa bleed steam from an exhaust steam of the high pressure turbine; and anaverage of feed-water temperature increases in second feed heaters wherea pressure of the feed water is lower than that of the first feedheater; falls within 1.9-3.5.

The invention according to claim 2 is a steam turbine cycle comprising ahigh pressure turbine, a reheating turbine, a boiler, feed heaters forheating a feed water to the boiler by a bleed steam from the highpressure turbine and the reheating turbine, a feed pump, and acondenser, the steam turbine cycle being a single-stage reheating cyclewhere a working fluid is water and using a Rankine cycle which is aregenerative cycle, wherein a steam temperature at an outlet of theboiler is 590° C. or more, and a specific enthalpy increase ratiobetween: a specific enthalpy increase in a feed water in a first feedheater corresponding to a bleed steam from an exhaust steam of the highpressure turbine; and an average of specific enthalpy increases in feedwaters in second feed heaters where a pressure of the feed water islower than that of the first feed heater; falls within 1.9-3.5.

The invention according to claim 3 is a steam turbine cycle comprising ahigh pressure turbine, a reheating turbine, a boiler, feed heaters forheating a feed water to the boiler by a bleed steam from the highpressure turbine and the reheating turbine, a feed pump, and acondenser, the steam turbine cycle being a single-stage reheating cyclewhere a working fluid is water and using a Rankine cycle which is aregenerative cycle,

wherein a steam temperature at an outlet of the boiler is 590° C. ormore, and a temperature increase ratio between: a feed-water temperatureincrease in a first feed heater corresponding to a bleed steam from anexhaust steam of the high pressure turbine; and an average of feed-watertemperature increases in feed heaters other than the first feed heater;falls within 1.9-3.5.

The invention according to claim 4 is a steam turbine cycle comprising ahigh pressure turbine, a reheating turbine, a boiler, feed heaters forheating a feed water to the boiler by a bleed steam from the highpressure turbine and the reheating turbine, a feed pump, and acondenser, the steam turbine cycle being a single-stage reheating cyclewhere a working fluid is water and using a Rankine cycle which is aregenerative cycle, wherein a steam temperature at an outlet of theboiler is 590° C. or more, and a specific enthalpy increase ratiobetween: a specific enthalpy increase in a feed water in a first feedheater corresponding to a bleed steam from an exhaust steam of the highpressure turbine; and an average of specific enthalpy increases in feedheaters other than the first feed heater; falls within 1.9-3.5.

EFFECT OF THE INVENTION

According to the present invention, there can be provided a steamturbine cycle of an improved cycle thermal efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of first to eighth embodiments and aneleventh embodiment of a steam turbine cycle of the present invention,and a conventional art;

FIG. 2 is a schematic view of ninth to eleventh embodiments of a steamturbine cycle of the present invention; and

FIG. 3 is a schematic view showing a relationship between a temperatureincrease ratio and a thermal efficiency.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A first embodiment of a steam turbine cycle of the present invention isdescribed below with reference to the drawings. FIG. 1 is a view of thefirst embodiment of the present invention.

The steam turbine cycle in this embodiment includes a high pressureturbine 1, a reheating turbine 24, a boiler 4, feed heaters 6 forheating a feed water to the boiler 4 by a bleed steam from the highpressure turbine 1 and the reheating turbine 24, a feed pump 12, and acondenser 10. The steam turbine cycle in this embodiment is asingle-stage reheating cycle where a working fluid is water and uses aRankine cycle which is a regenerative cycle.

A steam temperature at an outlet of the boiler 4 is 590° C. or above. Atemperature increase ratio between: a feed-water temperature increase ina first feed heater 7 corresponding to a bleed steam (high-pressureturbine exhaust bleed steam) 22 from a high-pressure turbine exhauststeam 21; and an average of feed-water temperature increases in secondfeed heaters 8 where a pressure of the feed water is lower than that ofthe first feed heater 7; falls within 1.9-3.5.

By adjusting a flowrate of each bleed steam 20 and each bleed position31, feed-water temperature increases in the first feed heater 7 and thesecond feed heaters 8 can be adjusted. In order to vary temperatures ofthe high-pressure turbine exhaust bleed steam 22 and anintermediate-pressure turbine exhaust bleed steam 32, exhaustspecifications of the high pressure turbine 1 and the intermediatepressure turbine 2 have to be changed.

A feed water temperature at an inlet of the boiler 4 is generallydefined by the boiler 4. Thus, with a feed-water temperature value beingfixed, an optimization calculation was conducted. Then, it was foundthat a cycle thermal efficiency becomes maximum under conditions thatthe temperature increase ratio falls within 1.9-3.5.

The temperature increase ratio between a feed-water temperature increasein the first feed heater 7 and an average of feed-water temperatureincreases in the second feed heaters 8 may vary within a certain range,depending on the number of the feed heaters 6, a mechanical differencein a steam turbine such as an exhaust loss, a value corresponding to apower generation output in a power plant, a difference in a minutestructure, and so on.

As described above, the non-patent document describes that an optimumspecific enthalpy ratio is 1.8. However, in a general power plant, aspecific enthalpy increase ratio of 1.8 is not practical as to a rangeof a temperature increase ratio.

A reason of this phenomenon is presumed as follows.

An output of the steam turbine is a sum of “a heat drop, i.e., aspecific enthalpy decrease amount×seam mass flowrate” at each stage ofeach turbine. Thus, it is more efficient when a steam is bled from aposition of a lower specific enthalpy as much as possible, because theboiler feed water 14 is heated after the steam turbine works. On theother hand, an efficiency of a regenerative cycle can be improved, whena temperature at the inlet of the boiler 4 of the boiler feed water 14is higher. Namely, both the efficiencies have to be considered.

When a temperature of the inlet of the boiler 4 is determined, there isrequired a steam of a saturated temperature which is substantially thesame as the inlet temperature of the boiler 4 of the feed heater 26 ofthe highest steam pressure. In this manner, a pressure of the bleedsteam 20 is determined. Other feed heaters 7 and 8 support stepwise thetemperature increase until the temperature reaches the value.

The high-pressure turbine exhaust bleed steam 22 is a steam that has alow specific enthalpy although a pressure thereof is relatively high. Inaddition, the high-pressure turbine exhaust bleed steam 22 is not ableed steam bled from a steam which has been heated by the reheater 5.Thus, when heating of the boiler feed water 14 with the use of theenthalpy of the high-pressure exhaust bleed steam 22 is increased, athermal efficiency of the overall cycle can be improved.

Namely, as schematically shown in FIG. 3, a temperature increase ratiohas a certain optimum value at which a thermal efficiency is maximized.This optimum value is preferable when the temperature increase ratio issufficiently higher than 1. This optimum value varies depending onconditions of the main steam 16, and it is presumed that the valuebecomes higher as to a steam of a higher temperature.

As described above, when a temperature increase ratio between: afeed-water temperature increase in the first feed heater 7 and; anaverage of feed-water temperature increases in the second feed heaters8; is set to fall within 1.9-3.5, a cycle thermal efficiency can beimproved.

Second Embodiment

Next, a second embodiment of the present invention is described withreference to FIG. 1.

A steam turbine cycle in this embodiment includes a high pressure a highpressure turbine 1, a reheating turbine 24, a boiler 4, feed heaters 6for heating a feed water to the boiler 4 by a bleed steam from the highpressure turbine 1 and the reheating turbine 24, a feed pump 12, and acondenser 10. The steam turbine cycle in this embodiment is asingle-stage reheating cycle where a working fluid is water and uses aRankine cycle which is a regenerative cycle.

A steam temperature at an outlet of the boiler 4 is 590° C. or above. Aspecific enthalpy increase ratio between: a specific enthalpy increaseof a feed water in a first feed heater 7 corresponding to ahigh-pressure turbine exhaust bleed steam 22; and an average of specificenthalpy increases of feed waters in second feed heaters 8 where apressure of the feed water is lower than that of the first feed heater7; falls within 1.9-3.5.

By adjusting a flowrate of each bleed steam 20 and each bleed position31, specific enthalpy increases in the feed waters in the first feedheater 7 and the second feed heaters 8 can be adjusted. In order to varyspecific enthalpies of the bleed steam 20 from a high-pressure turbineexhaust bleed steam 22 and an intermediate-pressure turbine exhaustbleed steam 32, exhaust specifications of the high pressure turbine 1and the intermediate pressure turbine 2 have to be changed.

A feed water temperature at an inlet of the boiler 4 is generallydefined by the boiler 4. Thus, with a feed-water temperature value beingfixed, an optimization calculation was conducted. Then, it was foundthat a cycle thermal efficiency becomes maximum under conditions that aspecific enthalpy increase ratio falls within 1.9-3.5.

A specific enthalpy increase ratio may vary within a certain range,depending on the number of the feed heaters 6, a mechanical differencein a steam turbine such as an exhaust loss, a value corresponding to apower generation output in a power plant, a difference in a minutestructure, and so on.

As described above, the non-patent document describes that an optimumspecific enthalpy ratio is 1.8. However, this document does not refer toa temperature of the main steam 16. Thus, since a different temperatureof the main steam 16 is assumed, an optimum value of a specific enthalpyincrease ratio is considered to be different.

Also in this embodiment similar to the first embodiment, asschematically shown in FIG. 3, a specific enthalpy increase ratio has acertain optimum value at which a thermal efficiency is optimized. Thisoptimum value is preferable when the specific enthalpy increase ratio issufficiently higher than 1. This optimum value varies depending onconditions of the main steam 16, and it is presumed that the valuebecomes higher as to a steam of a higher temperature.

As described above, when a specific enthalpy increase ratio between: aspecific enthalpy increase in a feed water in the first feed heater 7and; an average of specific enthalpy increases in feed waters in thesecond feed heaters 8; is set to fall within 1.9-3.5, a cycle thermalefficiency can be improved.

Third Embodiment

Next, a third embodiment of the present invention is described withreference to FIG. 1.

The steam turbine cycle in this embodiment includes a high pressureturbine 1, a reheating turbine 24, a boiler 4, a feed heaters 6 forheating a feed water to the boiler 4 by a bleed steam from the highpressure turbine 1 and the reheating turbine 24, a feed pump 12, and acondenser 10. The steam turbine cycle in this embodiment is asingle-stage reheating cycle where a working fluid is water and uses aRankine cycle which is a regenerative cycle.

A steam temperature at an outlet of the boiler 4 is 590° C. or more. Atemperature increase ratio between: a feed-water temperature increase ina first feed heater 7 corresponding to a high-pressure turbine exhaustbleed steam 22 and an average of feed-water temperature increases infeed heaters other than the first feed heater 7; falls within 1.9-3.5.

Herein, the feed heaters other than the first heed heater 7 mean thesecond feed heaters 8 where a pressure of the feed water is lower thanthat of the first feed heater 7, and a third feed heater 26 where apressure of the feed water is higher than that of the first feed heater7. The third feed heater 26 heats a feed water by a bleed steam from thehigh pressure turbine 1.

By adjusting a flowrate of each bleed steam 20 and each bleed position31, feed-water temperature increases in the first feed heater 7, thesecond feed heaters 8, and the third feed heater 26 can be adjusted. Inorder to vary temperatures of the high-pressure turbine exhaust bleedsteam 22 and an intermediate-pressure turbine exhaust bleed steam 32,exhaust specifications of the high pressure turbine 1 and theintermediate pressure turbine 2 have to be changed.

A feed water temperature at an inlet of the boiler 4 is generallydefined by the boiler 4. Thus, with a feed-water temperature value beingfixed, an optimization calculation was conducted. Then, it was foundthat a cycle thermal efficiency becomes maximum under conditions that atemperature increase ratio falls within 1.9-3.5.

A feed temperature increase ratio between: a feed-water temperatureincrease in the first heater 7; and an average of feed-water temperatureincreases in the feed heaters 8 and 26 other than the first feed heater7; may vary within a certain range, depending on the number of the feedheater 6, a mechanical difference in a steam turbine such as an exhaustloss, a value corresponding to a power generation output in a powerplant, a difference in a minute structure, and so on.

As described above, when a temperature increase ratio between: afeed-water temperature increase in the first feed heater 7; and anaverage of feed-water temperature increases in the feed heaters 8 and 26other than the first feed heater 7; is set to fall within 1.9-3.5, acycle thermal efficiency can be improved, similarly to the firstembodiment.

Fourth Embodiment

A fourth embodiment of the present invention is described with referenceto FIG. 1.

The steam turbine cycle in this embodiment includes a high pressureturbine 1, a reheating turbine 24, a boiler 4, feed heaters 6 forheating a feed water to the boiler 4 by a bleed steam from the highpressure turbine 1 and the reheating turbine 24, a feed pump 12, and acondenser 10. The steam turbine cycle in this embodiment is asingle-stage reheating cycle where a working fluid is water and uses aRankine cycle which is a regenerative cycle.

A steam temperature at an outlet of the boiler 4 is 590° C. or more. Aspecific enthalpy increase ratio between: a specific enthalpy increaseof a feed water in a first feed heater 7 corresponding to ahigh-pressure turbine exhaust bleed steam 22; and an average of specificenthalpy increases of feed waters in feed heaters 8 and 26 other thanthe first feed heater 7; falls within 1.9-3.5.

By adjusting a flowrate of each bleed steam 20 and each bleed position31, specific enthalpy increases in feed waters in the first feed heater7, the second feed heaters 8, and the third feed heater 26 can beadjusted. In order to vary specific enthalpies of the high-pressureturbine exhaust bleed steam 22 and an intermediate-pressure turbineexhaust bleed steam 32, exhaust specifications of the high pressureturbine 1 and the intermediate pressure turbine 2 have to be changed.

A feed water temperature at an inlet of the boiler 4 is generallydefined by the boiler 4. Thus, with a feed-water temperature value beingfixed, an optimization calculation was conducted. Then, it was foundthat a cycle thermal efficiency becomes maximum under conditions that aspecific enthalpy increase ratio falls within 1.9-3.5.

A specific enthalpy increase ratio between: a specific enthalpy increaseof a feed water in the first feed heater 7; and an average of specificenthalpy increases of feed waters in the feed heaters 8 and 26 otherthan the first feed heater 7 may vary within a certain range, dependingon the number of the feed heaters 6, mechanical differences in the steamturbines such as an exhaust loss, a value corresponding to a powergeneration output in a power plant, differences in minute structures,and so on.

As described above, when a specific enthalpy increase ratio between: aspecific enthalpy increase of a feed water in the first feed heater 7;and an average of specific enthalpy increases of feed waters in the feedheaters 8 and 26 other than the first feed heater 7; is set to fallwithin 1.9-3.5, a cycle thermal efficiency can be improved, similarly tothe second embodiment.

Fifth Embodiment

Next, a fifth embodiment of the present invention is described withreference to FIG. 1. The fifth embodiment shown in FIG. 1 differs fromthe first embodiment in that feed-water temperature increases in thesecond feed heaters 8 are calculated in consideration of a feed-watertemperature increase by a feed pump 12. Other structures of the fifthembodiment are substantially the same as those of the first embodiment.

Since the feed pump 12 heats a feed water, a temperature of the feedwater is increased. Thus, in consideration of the temperature increase,an average of a temperature increase in each of second feed heaters 8 iscalculated.

Alternatively, in the third embodiment, it is possible to calculatefeed-water temperature increases in the feed heaters 8 and 26 other thanthe first feed heater 7, in consideration of a feed-water temperatureincrease by the feed pump 12.

Also in this case, since the feed pump 12 heats a feed water, atemperature of the feed water is increased. Thus, in consideration ofthe temperature increase, an average of a temperature increase in eachof the feed heaters 8 and 26 is calculated.

A feed water temperature at an inlet of a boiler 4 is generally definedby the boiler 4. Thus, with a feed-water temperature value being fixed,an optimization calculation was conducted. Then, it was fond that acycle thermal efficiency becomes maximum under conditions that atemperature increase ratio falls within 1.9-3.5.

In addition to the reason as described in the first embodiment, atemperature increase ratio may vary within a certain range, underinfluences of a heat generation difference caused by a mechanicaldifference in the feed pump 12.

As described above, by calculating feed-water temperature increases inthe second feed heaters 8 in consideration of a temperature increase inthe feed water by the feed pump 12, and then by determining atemperature increase ratio, a cycle thermal efficiency can be increased,similarly to the first and third embodiments.

Sixth Embodiment

Next, a sixth embodiment of the present invention is described withreference to FIG. 1. The sixth embodiment shown in FIG. 1 differs fromthe first embodiment in that feed-water specific enthalpy increases inthe second feed heaters 8 are calculated in consideration of afeed-water specific enthalpy increase by a feed pump 12. Otherstructures of the sixth embodiment are substantially the same as thoseof the first embodiment.

The feed pump 12 increases a pressure of a feed water, andsimultaneously heats the feed water, as described in the thirdembodiment, so that a specific enthalpy of the feed water is increased.In consideration of the specific enthalpy increase, an average specificenthalpy increase in each of the second feed heaters 8 is calculated.

This embodiment can be carried out, in the above-described fourthembodiment, by calculating specific enthalpy increases of feed waters inthe feed heaters 8 and 26 other than a first feed heater 7, inconsideration of a specific enthalpy increase in a feed water by thefeed pump 12.

Also in this case, since the feed pump 12 increases a pressure of a feedwater, and simultaneously heats the feed water, so that a specificenthalpy of the feed water is increased. Thus, in consideration of thespecific enthalpy increase, an average specific enthalpy increase ineach of the feed heaters 8 and 26 other than the first feed heater 7 iscalculated.

A feed water temperature at an inlet of a boiler 4 is generally definedby the boiler 4. Thus, with a feed-water temperature value being fixed,an optimization calculation was conducted. Then, it was found that acycle thermal efficiency becomes maximum under conditions that aspecific enthalpy increase ratio falls within 1.9-3.5.

In addition to the reason as described in the first embodiment, aspecific enthalpy increase ratio may vary within a certain range, underinfluences of a heat generation difference caused by a mechanicaldifference in the feed pump 12.

As described above, by calculating a specific enthalpy increase in afeed water in consideration of a specific enthalpy increase in the feedwater by the feed pump 12, and then by determining a temperatureincrease ratio, a cycle thermal efficiency can be increased, similarlyto the second and fourth embodiments.

Seventh Embodiment

Next, a seventh embodiment of the present invention is described withreference to FIG. 1.

In the first embodiment, the third embodiment, and the fifth embodiment,the eight feed heaters 6 in total are used and a cycle structure is madesuch that a temperature increase ratio falls within 1.9-3.5. This isbecause, in a large heat power plant, the number of the feed heaters 6is preferably eight from an economical point of view.

In FIG. 1, steam is bled at two positions from the intermediate pressureturbine 2 including exhaust of steam, and steam is bled at fourpositions from the low pressure turbine 3. However, as long as the totalnumber of the bleed positions is six, the number and the positions arenot limited thereto.

In FIG. 1, a bleed steam to the aerator 9 is the intermediate-pressureturbine exhaust bleed steam 32, but is not limited thereto. With thenumber of the feed heaters 6 being limited to eight, an optimizationcalculation was conducted. Then, it was found that a cycle thermalefficiency becomes maximum under conditions that a temperature increaseratio falls within 1.9-3.5.

As described above, in the first embodiment, the third embodiment, andthe fifth embodiment, by using eight feed heaters 6 in total, and bymaking a cycle structure such that a temperature increase ratio fallswithin 1.9-3.5, a cycle thermal efficiency can be improved, similarly tothe first embodiment, third embodiment, and the fifth embodiment.

Eighth Embodiment

Next, an eighth embodiment of the present invention is described withreference to FIG. 1.

In the second embodiment, the fourth embodiment, and the sixthembodiment, the eight feed heaters 6 in total are used and a cyclestructure is made such that a specific enthalpy increase ratio fallswithin 1.9-3.5. This is because, in a large heat power plant, the numberof the feed heaters 6 is preferably eight from an economical point ofview.

In FIG. 1, steam is bled at two positions from the intermediate pressureturbine 2 including exhaust of steam, and steam is bled at fourpositions from the low pressure turbine 3. However, as long as the totalnumber of the bleed positions is six, the number and the positions arenot limited thereto.

In FIG. 1, a bleed steam to the aerator 9 is the intermediate-pressureturbine exhaust bleed steam 32, but is not limited thereto. With thenumber of the feed heaters 6 being limited to eight, an optimizationcalculation was conducted. Then, it was found that a cycle thermalefficiency becomes maximum under conditions that a specific enthalpyincrease ratio falls within 1.9-3.5.

As described above, in the first embodiment, the third embodiment, andthe fifth embodiment, by using eight feed heaters 6 in total, and bymaking a cycle structure such that a specific enthalpy increase ratiofalls within 1.9-3.5, a cycle thermal efficiency can be improved,similarly to the second embodiment, fourth embodiment, and the sixthembodiment.

Ninth Embodiment

Next, a ninth embodiment of the present invention is described withreference to FIG. 2. In FIG. 2, the same parts as those of FIG. 1 areshown by the same reference numbers, and their detailed description isomitted.

In this embodiment, by adding one feed heater 6 to the eight feedheaters 6 in total as in the above first embodiment, the thirdembodiment, and the fifth embodiment, the nine feed heaters 6 in totalare used, and a cycle structure is made such that a temperature increaseratio falls within 1.9-3.5. This is because, in a large heat powerplant, although the number of the feed heaters 6 is preferably eightfrom an economical point of view, there is a case in which the number ofthe feed heaters 6 is preferably nine, with a view to more increasing anefficiency, an output, and a temperature of a main steam.

In FIG. 2, steam is bled at three positions from an intermediatepressure turbine 2 including exhaust of steam, and steam is bled at fourpositions from a low pressure turbine 3. However, as long as the totalnumber of the bleed positions is seven, the number and the positions arenot limited thereto.

In FIG. 2, a bleed steam to a deaerator 9 is an intermediate pressureturbine exhaust steam 32, but is not limited thereto. With the number ofthe feed heaters 6 being limited to nine, an optimization calculationwas conducted. Then, it was found that a cycle thermal efficiencybecomes maximum under conditions that a temperature increase ratio fallswithin 1.9-3.5.

As described above, in this embodiment, by using the nine feed heaters 6in total by adding one feed heater 6 to the eight feed heaters 6 intotal as in the above first embodiment, the third embodiment, and thefifth embodiment, and by making a cycle structure such that atemperature increase ratio falls within 1.9-3.5, a cycle thermalefficiency can be improved, similarly to the first embodiment, the thirdembodiment, and the fifth embodiment.

Tenth Embodiment

Next, a tenth embodiment of the present invention is described withreference to FIG. 2.

In this embodiment, by adding one feed heater 6 to the eight feedheaters 6 in total as in the above second embodiment, the fourthembodiment, and the sixth embodiment, the nine feed heaters 6 in totalare used, and a cycle structure is made such that a specific enthalpyincrease ratio falls within 1.9-3.5. This is because, in a large heatpower plant, although the number of the feed heaters 6 is preferablyeight from an economical point of view, there is a case in which thenumber of the feed heaters 6 is preferably nine, with a view to moreincreasing an efficiency, an output, and a temperature of a main steam.

In FIG. 2, steam is bled at three positions from an intermediatepressure turbine 2 including exhaust of steam, and steam is bled at fourpositions from a low pressure turbine 3. However, as long as the totalnumber of the bleed positions is seven, the number and the positions arenot limited thereto.

In FIG. 2, a bleed steam to a deaerator 9 is an intermediate pressureturbine exhaust steam 32, but is not limited thereto. With the number ofthe feed heaters 6 being limited to nine, an optimization calculationwas conducted. Then, it was found that a cycle thermal efficiencybecomes maximum under conditions that a specific enthalpy increase ratiofalls within 1.9-3.5.

As described above, in this embodiment, by using the nine feed heaters 6in total by adding one feed heater 6 to the eight feed heaters 6 intotal as in the above second embodiment, the fourth embodiment, and thesixth embodiment, and by making a cycle structure such that a specificenthalpy increase ratio falls within 1.9-3.5, a cycle thermal efficiencycan be improved, similarly to the second embodiment, the fourthembodiment, and the sixth embodiment.

Eleventh Embodiment

Next, an eleventh embodiment of the present invention is described withreference to FIGS. 1 and 2.

In the first to tenth embodiments, a cycle structure is made such that asteam temperature at an outlet of the boiler 4 is 600° C. or more. Thisis because, when a temperature of the main steam 16 is 600° C. or above,a more significant effect can be expected. Namely, an effect ofimproving a cycle thermal efficiency due to an increased temperature ofthe main steam 16 is not damaged by set conditions of a bleed steam 20but can be fully exerted.

In the first to tenth embodiments, by making a cycle structure such thata steam temperature at an outlet of the boiler 4 is 600° C. or more, acycle thermal efficiency can be improved, similarly to the first totenth embodiments.

1. A steam turbine cycle comprising a high pressure turbine, a reheatingturbine, a boiler, feed heaters for heating a feed water to the boilerby a bleed steam from the high pressure turbine and the reheatingturbine, a feed pump, and a condenser, the steam turbine cycle being asingle-stage reheating cycle where a working fluid is water and using aRankine cycle which is a regenerative cycle, wherein a steam temperatureat an outlet of the boiler is 590° C. or more, and a temperatureincrease ratio between: a feed-water temperature increase in a firstfeed heater corresponding to a bleed steam from an exhaust steam of thehigh pressure turbine; and an average of feed-water temperatureincreases in second feed heaters where a pressure of the feed water islower than that of the first feed heater; falls within 1.9-3.5.
 2. Asteam turbine cycle comprising a high pressure turbine, a reheatingturbine, a boiler, feed heaters for heating a feed water to the boilerby a bleed steam from the high pressure turbine and the reheatingturbine, a feed pump, and a condenser, the steam turbine cycle being asingle-stage reheating cycle where a working fluid is water and using aRankine cycle which is a regenerative cycle, wherein a steam temperatureat an outlet of the boiler is 590° C. or more, and a specific enthalpyincrease ratio between: a specific enthalpy increase in a feed water ina first feed heater corresponding to a bleed steam from an exhaust steamof the high pressure turbine; and an average of specific enthalpyincreases in feed waters in second feed heaters where a pressure of thefeed water is lower than that of the first feed heater; falls within1.9-3.5.
 3. A steam turbine cycle comprising a high pressure turbine, areheating turbine, a boiler, feed heaters for heating a feed water tothe boiler by a bleed steam from the high pressure turbine and thereheating turbine, a feed pump, and a condenser, the steam turbine cyclebeing a single-stage reheating cycle where a working fluid is water andusing a Rankine cycle which is a regenerative cycle, wherein a steamtemperature at an outlet of the boiler is 590° C. or more, and atemperature increase ratio between: a feed-water temperature increase ina first feed heater corresponding to a bleed steam from an exhaust steamof the high pressure turbine; and an average of feed-water temperatureincreases in feed heaters other than the first feed heater; falls within1.9-3.5.
 4. A steam turbine cycle comprising a high pressure turbine, areheating turbine, a boiler, feed heaters for heating a feed water tothe boiler by a bleed steam from the high pressure turbine and thereheating turbine, a feed pump, and a condenser, the steam turbine cyclebeing a single-stage reheating cycle where a working fluid is water andusing a Rankine cycle which is a regenerative cycle, wherein a steamtemperature at an outlet of the boiler is 590° C. or more, and aspecific enthalpy increase ratio between: a specific enthalpy increasein a feed water in a first feed heater corresponding to a bleed steamfrom an exhaust steam of the high pressure turbine; and an average ofspecific enthalpy increases in feed heaters other than the first feedheater; falls within 1.9-3.5.
 5. The steam turbine cycle according toclaim 1, wherein the feed-water temperature increases in the second feedheaters are calculated, in consideration of a temperature increase inthe feed water by the feed pump.
 6. The steam turbine cycle according toclaim 2, wherein the specific enthalpy increases in feed waters in thesecond feed heaters are calculated, in consideration of a specificenthalpy increase in the feed water by the feed pump.
 7. The steamturbine cycle according to claim 1, wherein the total number of the feedheaters is eight, and the temperature increase ratio falls within1.9-3.5.
 8. The steam turbine cycle according to claim 2, wherein thetotal number of the feed heaters is eight, and the specific enthalpyincrease ratio falls within 1.9-3.5.
 9. The steam turbine cycleaccording to claim 1, wherein the total number of the feed heaters isnine, and the temperature increase ratio falls within 1.9-3.5.
 10. Thesteam turbine cycle according to claim 2, wherein the total number ofthe feed heaters is nine, and the specific enthalpy increase ratio fallswithin 1.9-3.5.
 11. The steam turbine cycle according to claim 1,wherein a steam temperature at an outlet of the boiler is 600° C. orabove.
 12. The steam turbine cycle according to claim 3, wherein thetotal number of the feed heaters is eight, and the temperature increaseratio falls within 1.9-3.5.
 13. The steam turbine cycle according toclaim 4, wherein the total number of the feed heaters is eight, and thespecific enthalpy increase ratio falls within 1.9-3.5.
 14. The steamturbine cycle according to claim 3, wherein the total number of the feedheaters is nine, and the temperature increase ratio falls within1.9-3.5.
 15. The steam turbine cycle according to claim 4, wherein thetotal number of the feed heaters is nine, and the specific enthalpyincrease ratio falls within 1.9-3.5.
 16. The steam turbine cycleaccording to claim 2, wherein a steam temperature at an outlet of theboiler is 600° C. or above.
 17. The steam turbine cycle according toclaim 3, wherein a steam temperature at an outlet of the boiler is 600°C. or above.
 18. The steam turbine cycle according to claim 4, wherein asteam temperature at an outlet of the boiler is 600° C. or above. 19.The steam turbine cycle according to claim 3, wherein the feed-watertemperature increases in the other feed heaters are calculated, inconsideration of a temperature increase in the feed water by the feedpump.
 20. The steam turbine cycle according to claim 4, wherein thespecific enthalpy increases in feed waters in the other feed heaters arecalculated, in consideration of a specific enthalpy increase in the feedwater by the feed pump.